We are studying control of expression globin genes by using a model system the K562 human leukemia cell line. We previously showed that these primitive cells can be reversibly induced by hemin to accumulate large amounts of embryonic and fetal hemoglobins in the absence of erythroid differentiation. Neither adult hemoglobin A, nor Beta-globin chains were observed. We studied the abundance and structure of specific mRNAs present in K562 cells both before and after induction of hemoglobin synthesis by hemin. In vitro translation generated protein products corresponding to Alpha, AGamma, GGamma, Epsilon and Zeta globin mRNA and indicated that the steady-state levels of these globin mRNAs increased 2-3 fold after induction, similar to the increases observed for globin. Thus, hemin induction of globin synthesis occurs at the transcriptional level. Similar results were obtained by S1 nuclease analysis. In addition, these studies revealed the presence of small amounts of Delta-globin RNA transcripts in K562 cells. No Beta-globin RNA was detected by this very sensitive assay. Previous studies by restriction endonuclease mapping suggested that the K562 Beta-globin locus had not suffered any major insertion deletions, or rearrangements. Therefore, we attempted to influence Beta-globin expression by growth of K562 cells in 5-azacytidine. The DNA of K562 cells became severely hypomethylated. We observed low levels of Beta-globin RNA transcripts by S1 nuclease mapping. However, Southern blot analysis of methyl-sensitive restriction enzyme digests showed no change in methylation at the two sites in the Delta-Beta-globin regions which can be studied. The mechanism of this effect will be studied, as well as the cellular factors required for expression of individual globin genes. The karyotype of K562 cells demonstrated triploidy. One of the chromosome 11 carried a translocation of varying length on the distal end of the short arm. Preliminary studies using in situ hybridization with [3H]-labelled globin probes suggest that this locus is intact; however, we are studying its relationship to the translocated genomic material and to cellular oncogenes.